Unipotential-cathode vacuum tube



Feb.; 4, 1930. w. H. 1-. HOLDEN UNIPOTENTIAL CATHODE VACUUM TUBE FiledDec. 19, 1924 INVENTOR WEZ'ZMie/w f ATTORNEY Patented Feb. 4, 1930PATENT OFFICE 'WILLIAI H. T. HOLDEN, OI BROOKLYN, NEW

PHONE AND TELEGRAPH COMPANY, A. CORPORATION OF NEW YORK YORK, ASBIGNOBTO AMERICAN TELE- UNIPOTENTIAL-CATHODE VACUUM TUBE Application MedDecember 19, 1924. Serial- No. 757,017.

g This invention relates to unipotential cathode vacuum tubes andparticularl to a tube of that type having a plurality of grid electrodesbetween the cathode and the plate electrode.

In the type of vacuum tube now widely used, the cathode which is of thefilament type is rendered electron-emitting by the conduction of acurrent therethrough. This method of rendering the cathode active,causes a drop in potential along the cathode which makes it diflicult tosatisfactorily employ alternating current for heating the oath-" ode,and has other disadvantages. There has accordingly been developed whatis known as a unipotential cathode tube in which the electron-emittingcathode is rendered active by an element separate and distinct from thecathode itself. This element may, for example, be a heater or it may bean electron-emitting device, rendering the cathode active bybombardment. The cost of producing unipotential cathode tubes isappreciably higher than tubes of the type heretofore employed and it isaccordingly desirable to employ them in a highly efiicient manner inorder to compete with the simpler and less expensive tube heretoforeemployed.

One of the objects of this invention consists in the provision of aplurality of grids in a vacuum tube of the unipotential cathode typewhereby a single tube of that type may e applied in a variety ofdifferent Ways to perform the function heretofore attainable onlythrough the use of a plurality of tubes of the type heretofore employed.e

Other objects of this invention will be apparent from the followingdescription when read in connection with the attached drawing, of whichFigure 1 is a cross-sectional view and Fig. 2 is a vertical view of thetube in which the invention is embodied. Fig. 3 is a schematic drawingof the electrodes of the tube, and Figs. 4,5 and 6 show various modes ofapplication of a tube of the form shown'in Figs. 1 to 3.

In Fig. 1, a heating element 1 is supported preferably at the center ofthe tube and is surrounded by the electron-emitting cathode 2. Thiscathode may be in the form of'a cylfor inder, either closed or open atthe top, and having its outer surface coated with electronemittingmaterial. Surrounding the cathode and concentric therewith are the grids3 and 4, grid 3 being spaced 2. definite interval from the cathode, andgrid 4 a definite distance from the grid 3. A plate electrode 5surrounds all of the other electrodes and is spaced a definite distancefrom the rid 4. All of the electrodes are enclosed wit in an evacuatedvessel 6. The various electrodes may be supported by means of lassarbors mounted upon the stem at the ase of the tube, and may beterminated in the base of the tube so as to be readily connected withthe conductors of the circuit in which tube is to be used.

The structure of the tube should be such that the voltage amplificationof the inner grid with respect to the plate, is smaller than that of theouter grid with respect to the plate. This may be accomplished inseveral ways known to those skilled in the art to which this inventionbelongs.

The manner in which the tube may be used is shown in Figs. 4 to 6inclusive. In Fig. 4 the tube is connected with an input circuit bymeans of a transformer 7 and with the output circuit by means of atransformer 8. A source 9 of alternating current is connected with theheating element 1 of the tube in order to energize this element so thatit in turn will cause the emission of electrons by the cathode tube. Thegrids 3 and 4 are strapped together and connected with the inputcircuit. The plate 5 is connected with the output circuit. The strappingtogether of the grids causes them to act as a single electrode. Such anarrangement produces high amplification, but also causes a highimpedance between the plate and the cathode of the output circuit. Thedegree of amplification attainable by a tube having a plurality of gridsconnectedin the. manner shown is greater than that attainable by a tubeof the type heretofore employed and consequently serves to reduce thenumber-of tubes required for high amplification.

The manner of using a double grid tube medium amplification and mediumplatecathode impedance is shown in Fig. 5. In this arrangement theoutermost grid 4 is connected by the switch arm 11 with the inputcircuit through contact 13 of switch 14 and the innermost grid 3 isconnected by the switch arm 12 with the'source of plate voltage throughcontact 15. In such an arrangement the inner grid, to which a positivepotential is applied, serves to reduce the tube impedance by reducingthe negative space charge around the cathode. The outer grid, to which anegative charge is applied by the battery 10, operates to control thespace current in the normal way. An arrangement such as shown alsopermits operation at relatively low plate voltages. he purpose of theswitch 14 will be fully explained hereinafter. i

The circuit shown in Fig 6 illustrates the manner of using the doublegrid tube when low amplification and low output impedance are desired.In this figure the inner grid 3 is connected with the input. circuit andthe outer grid 4 is connected in parallel with the plate 5. This mode ofuse increases the plate area and therefore tends to increase the cathodeemission. The inner grid is maintained at the negative potential bymeans of the battery 10. The low impedance of the output circuit, whichis attained by connecting the electrodes 4 and 5 in parallel, results ina fairly large current output at low amplification.

of a tube of the type shown in Figs. 1 to 3, various degrees ofamplification may be attained. By using the simple switching mechanismshown in Fig. 5 the several circuit connections shown in Figs. 4, 5, and6 may readily be established. When the switch 14 is thrown to the leftthe grids are connected as in Fig. 4 and when the switch is operated tothe right the grids are connected as in Fig. 6. It will be apparent thatvarious degrees of amplification may be obtained by varying the settingof the switch.

The arrangements shown in the figures illustrate schematically certainembodiments of the invention but it is obvious that the invention is notso limited but is capable of embodiment in other forms without departingfrom the spirit and scope of the appended claims.

What is claimed is:

1. In an electrical translating system, the combination with a vacuumtube comprising a unipotential cathode, two grids and a. plate, aheating element for the said cathode having a source of energy connectedtherewith, an input circuit connectedwith the cathode, an output circuitalso connected with the said cathode and with the said plate, andswitching means to connect the said input circuit and the said outputcircuit with the said grids in a predetermined manner.

It will be seen, therefore, that by means 2. An amplifier comprising avacuum tube hav ng an electron emitting cathode, a plate, and two gridsinterposed between said cathode and said plate, an input circuit and anoutput circuit, and switching means to control the connection of thesaid circuits with either of the said grids whereby the characterpf theamplifier may be determined.

In test1m ony whereof, I have signed my name to this specificationthisl7th day of 7 December, 1924.

' WILLIAM H. T. HOLDEN.

